The consumption and discharge of the flue gas, industrial raw material gas and other waste gases containing sulfur are increasing day by day due to the rapid development of industries. Discharge of waste gas containing sulfur has caused serious environmental pollutions, such as the formation of acid rain, acid corrosion of construction, respiratory diseases and skin diseases, etc., which are directly harmful to human health. Over years, scientific and technological researchers in various countries have intensively studied the desulfurization process of the flue gas, industrial raw material gas and other waste gases containing sulfur and accumulated a lot of research data. The desulfurization of the flue gas, industrial raw material gas and other waste gases containing sulfur has increasingly received much attention with the increased environmental consciousness. However, there are no significant progresses in the desulfurization techniques of the flue gas, industrial raw material gas and other waste gases containing sulfur till today. The desulfurization of the flue gas, industrial raw material gas and other waste gases containing sulfur is still a challenging problem.
The existing desulfurization processes of the flue gas, industrial raw material gas and other waste gases containing sulfur mainly include two types, wet desulfurization and dry desulfurization. The wet desulfurization specifically includes water washing method, limestone and limewater method, alkali metal solution method, alkaline solution method, ammonia method and alkylol amine method etc. The dry desulfurization specifically includes iron oxide method, zinc oxide method, manganese oxide method, cobalt oxide method, chromium oxide method, molybdenum oxide method, and activated carbon method etc. The water washing method, limestone and limewater method are mainly used in China. The limestone and limewater method, alkali metal solution method, alkaline solution method, ammonia method and alkylol amine method are widely used in developed countries. The water washing method has the disadvantages that a great deal of water is consumed, the used water cannot be recycled, serious secondary pollution has been caused by the discharge of waste water containing sulfur and the desulfurization effect is poor. The limestone and limewater method is better than the water washing method. However, the limestone and limewater method has the disadvantages of generating more solid wastes such as calcium sulfate, calcium sulfite and calcium carbonate, consuming a great deal of limestone and calcium oxide, huge equipment, large investment, and the equipment being inclined to be clogged due to the generated solid precipitates during the absorbing process. Further, calcium hydroxide is preferentially reacted with carbon dioxide during the absorbing process due to the limestone and calcium hydroxide having small solubilities in water, and then with sulfur oxides, thus the desulfurization effect of limewater method is not desirable. In addition, the limewater method has the disadvantages of more sewage discharge and serious secondary pollution. The alkali metal solution method, alkaline solution method, ammonia method and alkylol amine method are mainly used for the desulfurization of flue gas with relatively high content of sulfur dioxide (tail gases of smelting such as steel smelting and copper smelting, in which the sulfur dioxide content can be up to 8% or more), and the sulfur dioxide is recovered. These methods are not suitable for the desulfurization of normal flue gas due to the relatively high requirements for the techniques, relatively high energy consumption and high demand for material of the equipment. Meanwhile, corrosion to the equipment is dramatically serious for all the currently used desulfurization processes of the flue gas, industrial raw material gas and other waste gases containing sulfur.
So far, various gases are seldom subjected to desulfurization treatment before being discharged into atmosphere. The gases still have relatively high content of sulfur even if they are subjected to desulfurization treatment. The existing desulfurization methods such as HiPure method, Benfield method, G-V method, A.D.A method, water washing method, limestone and limewater method, alkali metal solution method, alkaline solution method, ammonia method, alkylol amine method, tannin extract method, and sulfolane method, as well as the dry desulfurization methods such as iron oxide method, zinc oxide method, manganese oxide method, cobalt oxide method, chromium oxide method, molybdenum oxide method, and activated carbon method are mainly used as primary desulfurization methods for removing hydrogen sulfide from industrial raw material gases, but are not commonly used for removing hydrogen sulfide from general gases. The main reasons for this are that these desulfurization methods have low desulfurization efficiency, high operating costs, high equipment investments, serious corrosion to equipment, undesirable desulfurization effects, and poor removal rate for organic sulfur[1-3]. The desulfurization technique by low-temperature methanol[4] is a method of physically adsorbing hydrogen sulfide, carbon oxysulfide, carbon disulfide and carbon dioxide and is commonly used for decarbonization and desulfurization of raw material gases in modern large-scale chemical enterprise. However, since methanol has low boiling point, is volatile, and has high saturated vapor pressure, it is usually required to operate under high pressure and at low temperature (less than −10° C.) and thus the energy consumption is high, methanol loss is serious, the process is complicated, the operation is tedious, and the comprehensive operating expense is high. The normal-temperature methanol method[5] is a method of absorbing hydrogen sulfide, carbon oxysulfide, carbon disulfide and carbon dioxide in gas by a mixed solution of 60% methanol and 40% diethanolamine and then releasing hydrogen sulfide, carbon oxysulfide, carbon disulfide and carbon dioxide by heating and reducing pressure. However, since methanol has low boiling point, is volatile, and has high saturated vapor pressure, the released gas contains a great deal of methanol, thereby resulting in variable solution composition and serious methanol loss. In addition, the chemical stability of the solution is poor for the reasons that the diethanolamine is prone to oxidative decomposition after being exposed to daylight and air. Therefore, the solution regenerating method has to be after the mixture of the hydrogen sulfide, carbon oxysulfide, carbon disulfide and carbon dioxide are regenerated and released by heating and reducing pressure, then using Claus method to convert the released gases containing sulfur into sulfur. This leads to high energy consumption, serious loss of methanol and diethanolamine, complicated process, tedious operation, and high comprehensive operating expense. The methods described above are mainly used for removing organic sulfur such as hydrogen sulfide, carbon oxysulfide, and carbon disulfide in gas, but not used for removing SO2 and/or SO3 in gas.
An equilibrium curve for an aqueous solution of glycerol (glycerin) absorbing sulfur dioxide was tested[6], and it was found that the aqueous solution has a poor absorption capability for sulfur dioxide, thus it cannot be directly used as the desulfurization agent for absorbing sulfur dioxide in flue gas; glycerol (glycerin) is added to an aqueous solution containing Cl− or an aqueous solution containing sodium hydroxide as a stabilizing agent for analyzing the content of sulfur dioxide in a gas[7-10], but it is not used as the desulfurization agent for removing sulfur dioxide in flue gas, and after the solution containing glycerol has absorbed sulfur dioxide, it cannot be regenerated to release the sulfur dioxide, thus the solution cannot be used as a solvent for flue gas desulfurization; A urotropine aqueous solution containing glycerol (glycerin) is also proposed to absorb SO2 in flue gas[11]. However, it is found that urotropine tends to be oxidative decomposed by oxygen gas present in the flue gas after contacting with it in practical experiment, causing the chemical property of the solution to be unstable. In addition, urotropine as a product of chemical and medical is expensive and is not readily available. Therefore, this method fails to be widely used due to high operating costs and unstable desulfurization performance.
A buffer solution of acetic acid and ammonia containing Fe2+ and Fe3+ [12-14] has been used for desulfurization of semi-water gas, which has relatively high desulfurization efficiency and relatively low corrosion. However, the solution is unstable due to ionic effect and salt effect. In the method of iron-alkaline solution catalyzed decarbonization, desulfurization, and decyanation from gas, an aqueous solution of alkaline substance containing iron ions is used for absorbing the sulfur in the gas. This method is capable of removing various types of sulfur and has better desulfurization effect than the conventional gas wet desulfurization method for the gas having low sulfur content. However, the iron ions are less stable in the alkaline solution and a large amount of precipitate of ferric hydroxide or ferrous hydroxide will be produced. Simultaneously, a large amount of precipitate of ferric sulfide or ferrous sulfide will be produced when the iron-alkaline solution is contacted with gas containing sulfide. Thus the content of iron ions in the solution decreases rapidly and the desulfurization effect significantly reduces. In addition, the phenomenon of clogging the desulfurization tower will occur. Therefore, this method is not suitable for the desulfurization of gas having high sulfur content[15]. In order to improve this situation, we attempt to carry out the desulfurization by “iron-alkaline solution” containing microorganisms under normal pressure or increased pressure and a good effect is achieved[16]. Furthermore, it is suggested to absorb hydrogen sulfide by ethylene glycol, or ethylene glycol ester, or diethylene glycol monomethyl ether solution. Then, sulfur dioxide gas is blown into the organic solution with absorbed hydrogen sulfide, and hydrogen sulfide is reacted with sulfur dioxide to produce sulfur so as to allow the organic solution to be regenerated and recycled for use[17-19]. Although the method for regenerating the ethylene glycol solution containing hydrogen sulfide by sulfur dioxide is very simple, sulfur dioxide is limited in supply and is not readily available. In addition, it is required for special device and safety measure during transportation. Therefore, this method has disadvantages that the operating cost is high and the safety measure is strict. It is proposed to absorb hydrogen sulfide, organic sulfur and water in natural gas or other gases by ethylene glycol solution, or a mixed solution of ethylene glycol and alkanolamine, or a mixed solution of ethylene glycol, alkanolamine, and sodium carbonate, or ethylene glycol dimethyl ether or diethanol dimethyl ether solution, or a mixed aqueous solution of diethylamine, diethylene glycol, triethylene glycol and triethylene glycol methyl ether, or a mixed solution of amine and acetaldehyde, or a mixed aqueous solution of diethylene glycol monomethyl ether and ferric nitrilotriacetate[20-28]. However, currently these processes described above are only used in the desulfurization of industrial raw material gas in large scale to remove hydrogen sulfide, carbon oxysulfide, and carbon disulfide in gas, but not used in the desulfurization of flue gas and other waste gases to remove SOx (including sulfur dioxide and/or sulfur trioxide). Our earlier patent techniques of “Method for removing SOx from gas by polyethylene glycol (Patent No. ZL200910009058.1)” and “Method for removing SOx from flue gas by ethylene glycol (Patent No. ZL200710110446.X)” have good desulfurization effects during practical industrialized production tests. However, during regeneration by heating, as the boiling point of ethylene glycol is only 197° C., there will be some loss of ethylene glycol, and meanwhile, a small amount of the ethylene glycol and polyethylene glycol solutions will deteriorate, which will increase the operating costs and affect desulfurization efficiencies. It has been found by further theoretical studies that sulfur dioxide or sulfur trioxide mainly interacts with hydroxyl groups in the molecules of ethylene glycol or polyethylene glycol and simultaneously is weakly bound to ether linkage in polyethylene glycol when interacting with ethylene glycol or polyethylene glycol. The interacting mechanisms are as follows: Taking ethylene glycol and diethylene glycol as examples only, the chemical reactions are as follows:

The following weak bindings will occur besides the above main reactions:

The following side reactions will occur during regeneration by heating:

From our current research results, it can be seen that these side reactions may be irreversible reactions. That is to say, there is so far no way to reverse these side reactions. The resulting sulfinate esters and sulfonate esters cannot be regenerated to release sulfur dioxide or sulfur trioxide. The capability of the solution to absorb sulfur will decrease as the amount of sulfinate esters and sulfonate esters in the solution increases. The solution deteriorates, thereby damaging the system and even making the system unworkable.